'I HAD to go to Ghana to learn that sick babies thrive best on their mothers' laps.' Those were the first words I heard from Cicely Williams, a fiery 90-plus, speaking from the floor in a packed meeting in Oxford. They exemplify the open, unconventional approach that made her a tremendous force in maternal and child health, a real pioneer of primary health care.

Williams went to Ghana, then the Gold Coast, in 1929, at a time when sick babies in British hospitals were separated from their mothers, and she found African mothers generally insisted on being with their babies, and that they recovered more quickly. A cuddle is worth a lot of medicine.

From her childhood experience of her own mother's 'back verandah clinic' at their home at Kew Park, Jamaica, Cicely Williams drew a familiarity with the common ailments of babies everywhere, exacerbated by poverty. She studied medicine during the First World War, when women were allowed to replace male students, emerging in the first batch of Oxford women medical graduates in 1923. But jobs for women doctors were in short supply as the men returned, and after a few years in house jobs she joined the Colonial Medical Service in 1929.

In the Gold Coast, one of a handful of women medical officers appointed to improve infant health, Williams was supposed to be engaged in preventive work in the clinics, but found demand for treatment of sick babies was overwhelming. On leave after six years, she wrote an MD thesis on child health - or rather disease - in the Gold Coast, based on the 100,000 cases she had treated there. During this period she had made the 'discovery' that was perhaps to bring her greatest fame - by careful observation and by listening to local people, Williams identified a condition of advanced malnutrition for which she used the African name (in the Ga language) kwashiorkor, or 'disease of the deposed child', associated with the loss of protein when a mother weans a toddler abruptly on the arrival of a new baby.

It took over 20 years for Cicely Williams's new disease to be fully recognised, and it gained acceptance only to become subject to further controversy. Is it lack of protein or simply lack of calories that leads to puffiness, flaking skin and rapid death? The opposition to her ideas arose partly from her position as a clinician practising 'out there' in the colonies; and partly from the fact that she was a woman. Her rueful comment on this epic battle was: 'These men in Harley Street couldn't believe you unless you wore stripy trousers.'

Transferred to Malaya in 1936, Cicely Williams campaigned against artificial infant-feeding. Incensed by milk companies sending girls in white coats around the tenements of Singapore, selling tinned milk as though they were promoting infant health, she delivered a stinging speech to the Singapore Rotary Club in 1939, uncompromisingly titled 'Milk and Murder'.

She also developed her concepts of an integrated preventive and curative health service for mothers and children. One of her great achievements was an experimental primary health scheme in Trengganu, in north-east Malaya, where a network of village health centres was set up with nurses trained to recognise the social aspects of disease, and indigenous midwives retrained in safer methods.

The report on Trengganu accompanied Cicely Williams into internment in Singapore's Changi Prison in 1942, following the Japanese invasion. She notes with pride that 20 babies born in Changi were all breast-fed and all survived. But she was taken by the Kemple Tai, the Japanese equivalent of the SS, to be held for nearly six months in conditions of appalling hardship. Although not tortured like the men with whom she shared a tiny cage, she was so malnourished that she lost a third of her body weight and developed beri-beri, leaving her to the end of her days with numbness in her feet. The only other woman in the cell, Freddy Bloom, swelled with beri-beri oedema till her trousers burst, and Williams wrapped her in her own sarong. Williams emerged physically bowed, with grey hair, but unbroken - and with a sense of mission.

After the war, recognition of her pioneering talents arrived; in 1948 she became first head of Mother and Child Health (MCH) at the nascent World Health Organisation in Geneva, and thence their head of MCH in south-east Asia. Her time here was curtailed by family illness, causing her to return to Jamaica for a spell in the early 1950s, but she was with WHO long enough to promote her vision of local resources as the key to improving the health of the poor, rather than 'first-world' models of health care that were highly technical and expensive. As she said: 'If you learn your nutrition from a biochemist, you're not likely to learn how essential it is to blow a baby's nose before expecting him to suck.'

At an age when most people would think about retirement, Cicely Williams continued with boundless energy in a career of research and teaching, in London, at the American University of Beirut, with the Family Planning Association, and Tulane University. She conducted surveys on child health in Borneo, Italy, Yugoslavia, Tanzania, Cyprus and Uganda. She worked with Palestinian mothers and children in the Gaza Strip. She lectured and advised on MCH in over 70 countries. In 1978, she retired 'except on demand' - and of course, she was very much in demand. From the 1950s on she was awarded many fellowships and tributes; at her 90th-birthday symposium at Somerville College, guest speakers - friends and admirers - assembled like an international Who's Who of MCH and nutrition.

One of the honours which charmed her most was the Honorary Doctorate of Science from the University of Ghana in 1986, with its citation describing her 'love, care and devotion to the sick children' and how 'within three weeks it became necessary to have the police keep order among the surging patients'. There is no doubt that, if I had been a Ghanaian mother with a sick child then, I should have 'surged' to see Cicely Williams.